It is likely that your systematic review will need to include a search of grey literature as well as the peer-reviewed journal articles found through database searching. Grey literature includes unpublished theses, conference proceedings, government reports, reports from professional bodies, unpublished trial data, and more. Leaving out grey literature can run the risk of biasing your results, as doctor and epidemiologist Ben Goldacre explains in the video below.
Searching grey literature can be challenging. Most sources of grey literature cannot be searched with complex Boolean searches the way you would search a database. The CADTH tool (link opens in a new window), which requires registration, for searching grey literature can help. There is also a useful journal article with supplementary files giving step-by-step instructions on how to search different sources of information for grey literature: Godin, K., Stapleton, J., Kirkpatrick, S.I. et al. Applying systematic review search methods to the grey literature: a case study examining guidelines for school-based breakfast programs in Canada. Syst Rev 4, 138 (2015) (link opens in new window).
The NHS Learning Academy have created a guide to Grey literature (link opens in new tab) which explains why and how to use grey literature and some sources of grey literature.
The range of organisations producing grey literature is massive - ranging from specialist organisations, government departments, professional bodies and pressure groups. Some examples are given below:
World Health Organisation - huge range of information including statistics and policy documents
Scottish Government - huge range of information including statistics and policy documents
Royal College of Nursing - professional body for the nursing profession
Scottish Public Health Observatory - part of Public Health Scotland includes health profiles, reports and papers
Resolution Foundation - think tank producing reports and influencing policy around UK living standards
Remember to bear in mind that materials produced by these bodies may be subject to bias.
These are good places to search for Grey Literature:
World Health Organization International Clinical Trials Registry Platform (ICTRP) (link opens in a new window): a searchable registry of clinical trials from all around the world
Sources of grey literature (link opens in new window) focused on research and policy documents from countries in the Global South
ScanMedicine (link opens in a new window): 11 clinical trials databases from across the world can be searched simultaneously.
UK Clinical Trials Gateway (link opens in a new window): a searchable database of non-commercial clinical trials
ClinicalTrials.gov (link opens in a new window): a registry of clinical trials in the US
Trials Register of Promoting Health Interventions (TRoPHI) (link opens in a new window): a searchable database containing details of over 7750 clinical trials, with a focus on public health
NICE Local Practice Case Studies (link opens in a new window): a collection of over 500 working examples of quality improvement in health and social care services
EThOS (link opens in a new window): the British Library's database of doctoral theses
The King's Fund Library (link opens in a new window): this collection incorporates the National Grey Literature Collection, and covers health and social care policy and management.
Social Care Online (link opens in a new window): grey literature for social care and social work - NB site no longer being updated BUT King's Fund Library is covering areas covered by this database.
Google Advanced Search (link opens in a new window): search for words appearing on specific websites and/or specific file types — very useful for finding reports, datasets and similar types of material. Lancaster University Library has created tips for filtering Google Advanced Search results to websites from specific countries (link opens in new window).
ASAPbio (link opens in a new window): publishing research before formal publication via preprint servers has become common. Getting information out quickly during the COVID pandemic was crucially important . A number of preprint servers have thus been established covering many subjects. ASAPbio list a range of these servers.
BASE (Bielefeld Academic Search Engine) (link opens in a new window): BASE is one of the world's biggest search engines for academic open access web resources. BASE is operated by Bielefeld University Library, in Germany.
Eldis (link opens in a new window): provides free access to relevant, up-to-date and diverse research on international development issues.
OAIster (link opens in a new window): an online union catalogue of open access materials.
OpenDOAR (link opens in a new window): an authoritative directory of academic open access repositories.
Social Science Research Network (link opens in a new window): provides rapid worldwide dissemination of social science research.
GreyNet (link opens in a new window): The goal of GreyNet is to facilitate dialogue, research, and communication between persons and organisations in the field of grey literature.
DANS (link opens in a new window): DANS is the Dutch national centre of expertise and repository for research data - includes, social sciences, archaeology, life and physical sciences..
Open Access Digital Theological Library (OADTL) (link opens in a new window): curate high-quality content in religious studies and related disciplines from publisher websites, institutional repositories, scholarly societies, archives, and stable public domain collections.
Archaeology Data Service (link opens in a new window): the leading accredited repository in the UK for archaeology and historic environment data.
CORE (link opens in a new window): an open access comprehensive bibliographic database of the world’s scholarly literature.
For any assistance/advice required please contact the Library Team at: hhsl@uhi.ac.uk